A conventional alarm known as a residential alarm is configured to detect emergencies such as a fire or a gas leak in a residence, and issues an alert by letting out a warning sound, for example. In recent years, multiple alarms are installed in one residence, and emergencies such as a fire are monitored for each room.
When multiple alarms are installed in a residence as described above, and an individual is present in a room separate from a room at which a fire occurs, the individual might not hear the warning sound, and a disaster such as the fire might spread. Thus, a suggestion for issuing a warning in coordination is made so that, the alarms are connected via a wire line, and when one alarm detects a fire, the alarm transmits a signal to another alarm and simultaneously lets out a warning sound (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2007-094719).
However, connecting the alarms via a wire line requires a power distribution work, leading to an increase in cost. This problem may be resolved by employing an alarm with radio transmission capability. Further, since the power consumption of recent ICs for a wireless circuit is decreasing, even if the alarm is in an operating mode so that transmission can be received at all times in order to be capable of receiving a signal from another alarm, a battery life exceeding five years, for instance, is installed, allowing practical use. Therefore, the practical application of a wireless-type alarm is spreading.
Incidentally, according to these types of alarms, an automatic checkup feature is provided to ensure that fires are monitored for an extended period of time. According to this automatic checkup feature, for example, an operating condition of a luminous element and a light receiving element provided on a smoke detection unit, which detects smoke due to fire, are examined, and it is determined periodically whether or not the alarm is normal or abnormal, and when the detection results indicates an abnormality, an alert is issued by letting out a warning sound or by illuminating an LED.